Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $222.95   8.336%   $241.5351   $241.54   $241.55   $241.50  
  Purchase #2 $90.62   11.296%   $100.8564   $100.86   $100.85   $100.90  
  Purchase #3 $56.53   4.305%   $58.9636   $58.96   $58.95   $59.00  
  Purchase #4 $202.90   11.175%   $225.5741   $225.57   $225.55   $225.60  
  Purchase #5 $139.68   8.400%   $151.4131   $151.41   $151.40   $151.40  
  Purchase #6 $134.64   10.702%   $149.0492   $149.05   $149.05   $149.00  
  Purchase #7 $204.63   11.822%   $228.8214   $228.82   $228.80   $228.80  
  7 purchase totals = $1,051.95       $1,156.2129   $1,156.21   $1,156.15   $1,156.20